1. Field of the Invention
This invention relates to implantable prostheses for joints such as knee, shoulder or other joints.
2. Background of the Invention
All joints of the body, including the knee, are vulnerable to injury and to damage by diseases. When joints are too diseased or injured for a microsurgical remedy, a prosthetic device may replace the joints. Since the 1970s, knee replacement surgery has offered persons with debilitating knee pain a chance to resume an active lifestyle. Also known as total knee arthroplasty, the procedure has become as successful as hip replacement surgery, which is considered to be one of this century's best-known medical advances.
The knee joint permits a wide range of motion that includes not only bending, but also sliding, gliding, and swiveling motions. This joint is also constructed to absorb the large forces generated during walking, running, and jumping maneuvers. Much like a hinge, the bottom end of the femur rests on top of the tibia, and when the knee bends, the ends of these two bones move against one another. Ligaments connect the femur to the tibia, while muscles and tendons stabilize the joint and enable it to move. The patella (knee cap) helps protect the joint and anchors important tendons.
Knee replacement surgery involves removing or resurfacing parts of the femur, tibia, and/or patella, and putting in a prosthesis made of metal alloy and high-density plastic. The most common reason for knee-replacement surgery is osteoarthritis, which causes a gradual deterioration of the cartilage between the tibia and femur, resulting in pain as the bones begin to rub together. Other reasons for knee surgery include rheumatoid arthritis (an autoimmune inflammation of the tissue surrounding the joints) and post-traumatic arthritis, which can occur years after an injury to the knee.
The prosthesis used in total knee arthroplasty will typically consist of several disconnected parts. One of the largest is fabricated out of a metal alloy, and attaches to the end of the femur after all diseased bone has been removed. Another major component, also fabricated of a metal alloy, resembles a tray on a pedestal. The pedestal is anchored into the tibia, and the platform has a surface of high-density plastic that acts as a bearing surface for the femur. If the patella has also been damaged, the knee replacement prosthesis may include a small circular piece of plastic that is attached to the patella, replacing cartilage and/or diseased bone.
In addition to the anchoring provided by having the metal prosthesis components physically inserted into bone tissue, two other techniques are available to insure a secure, durable connection between bone and prosthesis. A cementless prosthesis has a roughened, porous surface that is intended to enhance the ability of the bone tissue to grow directly into and around the metal component.
Cementless prosthesis unfortunately have shown a greater tendency for early loosening as well as for developing other long-term problems. The majority of orthopedic surgeons prefer to make use of bone cement to enhance the connection between the metal prosthesis members and the surrounding bone tissue. Methyl methacrylate is the most commonly used bone cement material.
In recent years there have been many improvements in techniques used for total knee arthroplasty. Nevertheless, tibial component loosening remains one or the most frequent modes of failure. Studies have indicated that bone cement pressurization and penetration are factors for increasing the strength of the bone-prosthesis interface. Present methods provide for relatively good cement penetration in the central areas of the bone-prosthesis interface. Unfortunately, leakage of cement around the periphery of the metal component during insertion results in relatively poor cement penetration around the outer edges of the prosthesis. Studies have suggested that a uniform cement penetration of 3-5 mm over the entire bone surface is desirable when attaching the prosthesis member to the underlying bone tissue.
It is an object of our invention to provide an apparatus for use with an orthopedic prosthesis for controlling and compressing cement during implantation of the prosthesis to provide uniform cement penetration.
It is also an object of our invention to provide a kit comprising an orthopedic prosthesis and a ring adapted to engage the prosthesis while cement is used to secure the prosthesis to bone such that a more secure and uniform cement mantel is formed.
It is further an object of our invention to provide a method for installing an orthopedic prosthesis whereby a more uniform cement penetration can be obtained.